JBL SRX700 Series Speakers
By Mark Amundson
Of all the club rigs I run into, installed or portable, the JBL SR4700 series has been the most frequent occurrence. And no wonder, with large SR4719 subwoofers having dual 18 drivers, and the popular SR4732 tops featuring dual 12-inch mids, 2-inch throat drivers and the very high frequency "baby butt" tweeters, covering the audio bands nicely. But with all this popularity, plus improvements through three updates, where do you go next? JBL came up with the SRX700 series to fend off encroaching competition, and to steal a few competitive ideas as well. First on the list was to insert the new dual voice coils and neodymium magnets on the low frequency drivers, and switch to neodymium on the high frequency drivers. This all drops weight. Consequently, the bigger SR4732 morphed into a smaller, lighter SRX722 cabinet design, featuring all-birch plywood (like the SR4732) beneath the Duraflex finish and 16-guage powder coated grilles.
The SRX728S dual 18-inch subwoofer also got a makeover from its SR4719 origins, by using birch plywood and making the front baffle hug the drivers a little more closely. Usually this means a sacrifice in box volume and low frequency response, but the JBL engineers gave the SRX728S nearly three feet of backside to ensure a -3dB corner down to 33Hz for plenty of seismic sensation. I received a pair each of the SRX722 and SRX728S cabinets for this road test.
SRX728S Subwoofer
The SRX728S subwoofer cabinet is meant for horizontal positioning, with rubber feet only along the long dimension (23.7" by 42" by 33") and venting across the same length. As a handy measure, the SRX728S also has rubber feet recesses on the top for stacking another SRX728 above. Of course, you can go vertical to put the SRX722 higher, but the duraflex exterior is then in direct contact with the floor.
In checking out the electrical interface (jackplate) of the SRX728, an immediate smile came to my face when I saw the slide switch for connecting the drivers to either the +/-1 contacts or +/-2 contacts of the NL4 Speakon connectors. Experienced SR4719 users will understand that JBL produced early versions with the +/-2 contacts wired, before later switching to the +/-1 contacts. This caused some confusion for a while, and I remember having to either have dedicated subwoofer cabling, or take precious time to rewire cables in the field for the subwoofer-side Speakons to +/-2 operation. The original rationale for +/-2 subwoofers was that a single four-wire speaker cable could chain both tops and subs, for +/-1 contacts to passive driven tops and +/-2 contacts for subs. Now users can still take advantage of this feature, or go back to conventional cabling.
The SRX728 has a frequency response of 27Hz to 220Hz (-10dB) with a nominal sensitivity of 98dB SPL at one watt/one meter. To make up for the modest sensitivity, you can put a lot of watts into the SRX728, with its 3,200-watt program rating and 6,400-watt peak power rating at four ohms. And you wondered why Harman (Crown) now has I-Tech amps with 4,000-watt at 4-ohm capability. All these watts are handled by two differential-drive 2268H drivers with the neodymium magnet motors. (JBL responds: "The sensitivity spec doesn't tell the entire story. We made a decision to specify the sensitivity only in the frequency band in which a subwoofer is actually used. It is common for other subs to have a sensitivity spec that is inflated by the higher sensitivity of the driver at frequencies far above those at which a subwoofer usually works.")
SRX722 Top Boxes
The JBL SRX722 top boxes have a 70Hz to 20kHz (-10dB) frequency response and a sensitivity of 97dB SPL at one watt/one meter that matches up well with the subwoofers. The dual 12-inch mid-bass drivers handle 2,400 watts program and 4,800 watts peak power. On the higher frequency side, the 4-inch voice coil/2-inch throat of the 2451H HF driver handles 150 watts program, and 300 watts peak at eight ohms of nominal impedance. A jackplate-mounted switch allows for quick selection of passive or bi-amp mode of operation. In passive mode, only the +/-1 contacts are connected, with the +/-2 contacts just wired through on the NL4 Speakons.
Tune-ing
JBL's Web site provides tunings for the SRX700 series speakers used in bi-amp mode for stand-alone usage or top/subwoofer combinations. For my review, I first used the recommended settings, then reverted to a shop pink noise/RTA process to see if I could improve upon things. The SRX728 subwoofer was tuned for 31 to 81Hz with a Butterworth 18dB/octave filter on the low side and a 48dB/octave Linkwitz-Riley filter on the high side. Two small upward pushes at 42 and 68Hz were recommended for taste on the parametric filters.
The SRX722 top got 81Hz and up with a 48dB/octave Linkwitz-Riley at 1.12kHz between the drivers. After a -10dB drop for the HF driver sensitivity match, small parametric dips were inserted at 650Hz and 1.6kHz for taste. The HF compensation was implemented with a 9dB/octave shelving filter starting at 6.54kHz to +5.5dB boost.
In Use
Before the gigs, I found the experience using CD tracks very nice, but thought I could achieve a notch better. After running a pink noise and RTA sweep, I made some slightly different parametric filter tweaks and got my experience improved. I did change the HF shelving and put a bit more gain above 10kHz to push the 2451H driver for flatter response to 12kHz. I felt I needed a bit more sizzle before admitting defeat in the 10kHz and up response. It also left me thinking how the JBL SRX722 would sound if the smaller 2431H driver (with the lighter 3-inch voice coil) was substituted for more upper frequency support.
Out at a few club gigs, the SRX700 boxes proved to be fine performers, and I especially liked the SRX722's 75- by 50-degree pattern horn for medium throws. The SRX728S has a lot going for it, with better performance and plenty of power handling headroom. Previously, I could easily over-exert SR4719s, but you will run out of watts into the SRX728S before Xmax happens. Overall, the SRX700 cabs are worthy for most professional sound reinforcement uses.
What it is: Tops and subs for clubs and smaller outdoor uses
Who it's for: Users desiring the JBL sound with a touch more portability and performance
Pros: Lighter weight, rugged speakers with a good, loud sound
Cons: Could use a HF driver with a bit more range up top
How much: JBL SRX722 $1,799; SRX722F (flying version) $2,099; SRX728S $1,599
Sabine FBX2400
By Paul Overson
Feedback killers suffer from an image problem. Too many sound people look down on anyone with one in the rack as being some kind of amateur who can't tune a system properly and needs a "crutch" to get through the gig. But most of us in the trenches are regularly called on to provide sound on gigs where speaker and mic placement is less than ideal, and feedback can become an issue pretty quickly. And just try arguing with the event planner who wants the sound system to be invisible about getting those speaker stacks moved out in front of the mic line. Sometimes a tool like this is just what the job requires.
The Gear
The Sabine FBX2400 Dual Channel Feedback Exterminator is an elegant yet simple feedback controller. It features two channels of 12 independent digital notch filters. These filters are 1/10 or 1/5 octave (user selectable), constant "Q" (filter skirts do not widen as the filters get deeper) from 40Hz to 20KHz. The time required to find and eliminate feedback is typically 0.4 seconds @ 1KHz. It has two types of user-selectable notch filters: "fixed" or "dynamic." The fixed filters remain set on the initial feedback frequencies, while the dynamic filters are automatically assigned with new frequencies as feed-back occurs during the program. The dynamic filter timer resets in one, five, 30 or 60 minutes.
The unit includes the following for each channel: an Active/Bypass button and LED indicator, which allow the user to set the unit to control feedback (active mode) or take the unit out of the signal path so it has no effect on the program (bypass mode); signal level LEDs, which indicate the signal strength relative to FBX's input clip level; a Setup button so all filters may be re-configured; a Reset Dynamics button to manually or automatically reset the dynamic filters; a Number Fixed button to select the total number of fixed filters to be activated; a Ready button and blue LED indicator, which allows the user to lock filters created during system set-up and to limit the total number of active filters, a Fifth Octave button to select wider filters; and a row filter stage activity LEDs to indicate active filters. Enough of the specs–let's get on with the "real world" use of the unit.
The Gigs
I used the FBX2400 on a middle school play (The Music Man) in which the downstage center was directly under a speaker cluster of three large-format 2-inch horns and two 15-inch speaker boxes. The students were trained to project their voices, but few of them really did project well enough to be heard. Eight wireless lavalier mics were used on the lead actors, but theses mics were constantly being changed from one actor to another. It was very difficult to mix the constant changing dynamics until I inserted the FBX2400 into a lavalier mic group. The controller immediately found three filters (automatic mode) and then during the rest of the performance, it found a total of nine filters. I used the FBX2400 on four performances, and each time it found seven to nine filters in the automatic mode. During one scene, three wireless lavs were used by actors on a walking bridge (directly under the speaker cluster), which raised the mics even closer to the speakers (less than six feet below). It was a love scene, so none of the actors were projecting their voices. I was very grateful to use the FBX2400 for this gig because I experienced no feedback during the performances.
The next gig was a U.S Air Force ROTC "Spring Dining Out" in which the condenser mic at the podium was in front of the speaker stacks. I again set it on automatic mode and rang out the podium mic. The FBX2400 again found nine filters. I have used other brands of feedback controllers, and when more than six filters were used, the sound was noticeably different. In the both cases with the Sabine unit, I could hear a small difference, but it was almost imperceptible.
What it is: Stereo feedback killer with 12 filters available per channel
Who it's for: Anyone working in the real world
Pros: Easy to set up and use. Minimal coloration of overall sound
Cons: None
How Much: MSRP $499.95
Sencore SP295 Analyzer
By Paul Overson
The Sencore SP295 SoundPro Contractor is a quality, high-end audio and acoustic analyzer designed for audio professionals, commercial audio installers, audio system engineers and civil engineers. It utilizes DSP technology, FFT analysis and octave-based filters for accurate, real-time acoustic analysis.
The unit is hand-held, which enables the user to walk around a venue and analyze audio from anywhere. Some of the functions include: Filter Real-Time Analyzer, FFT Real-Time Analyzer, Energy Time Graph, Reverb Decay Time, Sound Study Graph, Sound Level Meter, Noise Criteria, Signal-to-Noise Ratio, Distortion Meter, Polarity Test, Signal Generator, Sweeps and much more.
I used this instrument for a country band concert in a middle school lunch "cafetorium." The room was about as bad as I have ever seen. The stage has a low ceiling and steps leading down into a sunken seating area surrounded by five-foot high concrete walls. The rest of the seating area is above the walled portion, with bleachers placed in the back. Seating also extends on walkways around the sides of the sunken area. The ceiling in the seating area is exposed trussing. The only place for the ground-stacked speakers was in the sunken area in front of the stage. We laid speaker boxes (unplugged, just for height) on their sides and placed bass boxes on top of the laid-down cabinets, with mid-high boxes stacked on top of the bass boxes (sub bass, bass and mid-high). The whole idea was to get the sound as high as possible. We used the SP295 C FFT Real-Time Analyzer to see which frequencies were bouncing around the room so we could eliminate them when possible. We also used the Reverb Decay Time to measure sound from the solid surfaces that surrounded the concert area. The school asked us to have the sound pressure level around 100 dB, so we used the SP295 C to check on that as well.
The gig went well. The school administration was happy and the band was very pleased with the results. On a side note, I measured the kids screaming in excess of 110 dB. It was really loud!
I was very pleased with all of the capability of the SP295 C. I used it for testing cables, generating pink noise, sound level meter, FFT RTA, reverb decay time and a sound study graph. I found each of these functions to be easy to use, accurate and helpful. I could walk around and check various areas to see what the differences were. The battery pack has sufficient power to run for approximately two hours, depending on how it is used. I have used handheld RTA units before, but the SP295 C is much, much more. This unit is equipped with a microphone, XLR and 1/4-inch left and right inputs, RCA phono unbalanced left and right inputs, XLR balanced mono output, 1/4-inch balanced mono output, RCA phono unbalanced mono output, 1/4-inch stereo headphone output and a serial interface for hooking it up to a PC. It also has a speaker and a small 64- by 128-pixel super-twist LCD with an LED backlight display system. The SP295 C also comes with a power adaptor and non-volatile memory for storing 40 graph data locations. The SP295 C weighs just three pounds five ounces and is 10 3/8" by 6" by 3 1/2" (HWD).
I stored an FFT RTA graph and recalled it to see what happened, and it displayed just fine. The unit is very well made and looks attractive as well. I had some trouble seeing the graphs without the backlight on when in a dark venue. I was able to move the cursor and then the backlight would light up.
The SP295 C is well-made, versatile, portable and performs as designed. I recommend this unit for installers and those who need to have one device that can do a variety of functions. The only trouble I experienced was the relay from the power adapter jack, which sometimes stuck, resulting in not being able to turn the unit on using the battery. Sencore assisted me immediately with a solution. The fix was easy in that all I had to do was plug in the power adapter and then turn the unit on, then remove the power adapter. I understand that this problem has been re-engineered for future models. Sencore assisted me with any questions that I had and as previously mentioned, gave me a solution to the only problem I encountered.
What it is: Multi-function audio analyzer
Who it's for: Installers and anyone working in difficult acoustic environments
Pros: Flexible, durable and pretty easy to figure out
Cons: Not cheap, had problem with the power adapter (fixed with direction from the manufacturer)
Cool Tools
Hear Technologies Hearbuds
By Bill Evans
Anyone who has been reading FOH for any time at all knows that I am a big fan of the Hearback personal monitoring system–to the point that I bought one and use it at every rehearsal and most gigs I do as a player and carry it to any sound gig I do where I have to provide both FOH and monitors form a single location. Using the Hear mixing system and a handful of universal-fit PM earpieces, I have converted many a wedge-lover to the joys of personal monitoring. But the hardest part of that has been keeping up with the foam sleeves that go on all of the earpieces. They are basically good for one use (unless the same person is using them all the time, and then his life depends on your grunge-tolerance) and every manufacturer's sleeves have a different inner diameter, so you have to keep a bunch of different ones on hand.
Eliminating the foam is one of the big things I like about the Hearbuds. They look like the kind of consumer ear buds you see people using with an iPod, but there is a soft plastic sleeve that fits over it and inserts into the ear canal for an experience somewhere between the foam thing and a custom-fit PM. The sleeves come in three sizes for small, medium and Dumbo-sized ears. They sound good, have a 10- foot cable (something I wish the high-end PM ear-piece makers would consider), and getting them ready for a new user just means whipping out one of those sterilizing hand-wipes and making sure it is clean. I like them enough that, while I have two sets of custom PMs, when I plugged these in to check them out, they stayed in use until someone else needed them. Hearbuds MSRP $14.99; Hearbuds and headset MSRP $39.95.
Radial PRO DI Direct Box
By Mark Amundson
Radial Engineering has been known for many flavors of passive and active Direct Inject (DI) boxes, including its Jensen Transformer equipped "JDI" direct box. While the JDI is popular in national soundco mic lockers, its couple-hundred-dollar price tag has kept sales down to the very serious user. So taking the hint, Radial Engineering has come up with an economy version of the JDI, called the PRO DI.
The Radial PRO DI is a smaller version of the JDI with fewer features (no input merge or output polarity flip), but retains the same quality switches and jacks as its big brother. While not as fully specified as the JDI, the PRO DI still maintains the 140k-ohm input impedance (1k-ohm output reference), and even improves upon the distortion rating to less than 0.01% from 20Hz to 20kHz. Without the -15dB pad switch engaged, the PRO DI can accept just about any pro-audio level sent to it, with just a -22dB drop for impedance matching.
The PRO DI, using my Neutrik Minirator and Minilyzer test equipment, handily exceeded the +/-2.5dB spec and kept within 0.2dB flatness across a 20Hz to 20kHz sweep. In checking distortion, it was apparent that my audio sources were much worse than the 0.01% spec. But even with that handicap, I was able to check +22dBu across the 20Hz and up audio bands. Most direct boxes are adequate at +10dBu on the low frequencies, but with the PRO DI, only at the 20Hz to 40Hz corner with above +20dBu levels was I able to add 0.02% more distortion. Quite impressive for a $99 MSRP DI box.
In gigging, I put a Radial PRO DI on keyboards and acoustic guitar duties, as that is the prime usage for passive direct boxes. While no differences were detected in the maelstrom of rock 'n' roll performance, I was able to PFL the individual channels with the PRO DI and critically listen. In these sneak listen PFLs and quieter ballads, the transparency of the PRO DI was noticeable, and more open than DI boxes with smaller, cheaper transformers. I am sorry to say, my other popular brand passive DI boxes are going collect some dust from here on.
Visual Sound 1 Spot
By Bill Evans
One of the acts I do some work for walks into every gig and hands me a "wireless" rack; a four-space SKB with a Furman Rack Rider and four half-rack wireless receiver units for three guitar players and one fiddler. None of the units suck, but they all are of the high-end MI grade, which means wall warts instead of an internal power supply. I could manage to get all four of those black boxes onto the Rack Rider, but there was not a lot of space to spare.
Recently, these guys have discovered the joys of personal monitors, and three of them have switched over. There was no way I could get more wall warts onto that power strip. Enter the 1 Spot for Wireless from Visual Sound (www.visualsound.net), an AC adapter that puts out 12 volts with enough juice to power up to five wireless units all by itself… and it only takes up one space on that Rack Rider.
The 1 Spot runs about 25 bucks, and the five-way adapter cable another $10. With an output of 1500mA, it will handle most wireless units out there, and it automatically converts voltage in case you are touring in places where 120 is not the norm. Even if you don't need to save power strip space, the 1 Spot makes for a great emergency wall wart replacement. They also make a 9-volt version for stompboxes and adapters for older and odd-sized power jacks. For $35, it makes for one hell of an insurance policy.
